Cytotaxonomical studies in Indian Dendrobiums (Orchidaceae)

Abstract

Twenty different species of Indian Dendrobiums are collected from the Western Ghats and North Eastern India was evaluated cytotaxonomically. Out of the twenty species, eleven species had 2n=38 chromosomes and nine had 2n=40 chromosomes. All the species endemic to Western Ghat region had 2n=38 (n=19) chromosomes, but the species from Eastern India had both 2n=38 as well as 2n=40 (n=19, 20) chromosomes. Chromosomes were found to be very small in size in this genus. Length of chromosomes ranged between 2.75 pm in D.herbaceum and 4.5 pm in D.aggregatum. Size of chromosomes ranged between2.0 and 2.75 pm in other species. In this investigation karyotypes were not much helpful in delineating different species from each other. Species having close morphological similarity had very distinct unrelated karyotypes. Out of the twenty species studied, five species showed the presence of satellites, mostly one pair except in D.nobile which had two pairs of satellite chromosomes. The satellites were very distinct and hint towards the polyploidy origin of the species. The differentiation of Dendrobium species as evident by karyotypic variation may be due to the increase in telocentric chromosomes by centric fission or simple translation or inversion. However, the structural changes in chromosomes appear to have little effect on the external morphology of different species